TWEAK is a ligand in the TNF family that could potentially serve as a secreted mediator. Mouse TWEAK was identified in 1996 as a novel ligand in the TNF family by Yves Chicheporliche during an examination of potential erylhropoielin-related transcripts (Chicheportiche el a/., 1997). A partial human homolog was identified in the EST database and. using this sequence, a full-length human cDNA was cloned from a tonsil library. Following on the observation that TWEAK can induce cell death only in the presence of IFN7 or weakly in a very limited set of cells, the designation TWEAK was given, reflecting the TNF family relationship and the weak death.